1. Field of the Invention
The present invention relates to optical pickups for reading and writing information to and from an optical recording medium, such as an optical disk, and to lens holders used in such an optical pickup.
2. Description of the Related Art
Generally, an optical pickup of this kind has a laser light source for emitting a laser beam and optics for guiding the emitted laser beam to a recording medium such as an optical disk. A rewritable recording medium, such as CD-Recordable or CD-Rewritable, permits reading of information, as well as writing of information. With an optical pickup for CD-Recordable, it is necessary to switch the output level of the laser beam emitted from a laser light source, depending on whether information is read or written, for the following reason. To write information, laser beam is radiated to form pits in the recording layer of an optical disk. The output of the laser beam is emitted from the laser light source during writing of information and is higher than the output emitted during reading of information. For example, the former output is about 10 to 20 times as large as the latter output.
An optical pickup used for an optical disk drive, such as a CD recorder, comprises an optical base, a lens holder, a damper base connected to the lens holder via suspension wires, and an actuator base that accommodates both lens holder and damper base. The lens holder is equipped with an objective lens, a tracking coil, and a focusing coil. The actuator is formed integrally with a yoke having a magnet for driving the lens holder by making use of the interaction between the tracking coil and the focusing coil.
The optical pickup has a laser acting as a light source that emits a laser beam. The laser beam emitted from the laser is made to hit an optical disk, such as a CD-R disk, that is an optical recording medium through a diffraction grating, a beam splitter, a collimator lens, and an objective lens. Light reflected from the optical disk impinges on a photodiode (PD) that is a light-receiving device through the objective lens, the collimator lens, and the beam splitter. That is, the photodiode receives the light reflected from the optical disk. Optical parts include the laser and the beam splitter and are held to the optical base.
The lens holder of the objective lens has flat support portions, a seat portion cylindrically protruding from parts of the flat supports, and the aforementioned objective lens installed on the seat portion. The seat portion is provided with crisscross grooves extending diametrically. Claws protrude upward from the grooves.
The optical lens of the optical pickup and the lens holder for holding the pickup are bonded together by placing the objective lens on the flat top-end surface of the seat portion of the lens holder and using an adhesive, such as a UV-curable resin.
If the flat top-end surface of the seat portion on which the objective lens is to be placed is partially concave, the adhesive may soak through the objective lens toward its center. If this adhesive reaches a portion of the objective lens through which light can pass (hereinafter referred to as the effective region of the objective lens), the optical characteristics of the pickup will deteriorate.
It is an object of the present invention to provide a lens holder capable of firmly holding the objective lens of an optical pickup to the holder via an adhesive without contamination of the effective range of the objective lens due to the adhesive.
It is another object of the invention to provide an optical pickup for use in the lens holder described in the immediately preceding paragraph.
According to one aspect of the present invention, there is provided an optical pick up which has a lens holder on which an objective lens is held, an actuator base, a damper base connected to the actuator base, and suspension wires. The lens holder has a seat portion for locking said objective lens. The seat portion has a top-end surface.
In the aspect of the present invention, an inclined surface is formed in said top-end surface of said seat portion and sinking outward.
According to another aspect of the present invention, there is provides a lens holder which has a seat portion for locking an objective lens of an optical pick up. The seat portion has a top-end surface that is an inclined surface sinking outward.
Other objects and features of the invention will appear in the course of the description thereof, which follows.